Tribology properties emerge from a variety of mechanisms occurring along the sliding surfaces, at different length scales and time scales. Engineering friction and wear laws are mostly empirical, fitted against experimental results and thus only valid on a limited range. This talk aims at discussing recent progress in uncovering the physics behind tribological processes using molecular dynamics (MD) simulations. Using model interatomic potentials whose tail can be adjusted to change the behavior from ductile to brittle without affecting the small strain elastic properties, the onset of wear is modeled at the atomic scale. Simulation of a single contact junction, for the case of homogeneous material, has permitted to establish and validate a critical contact length scale that governs debris formation. This length scale is based on material parameters. Running the simulations for long time scales leads to the appearance of self-affine surfaces similar to the ones observed in nature. This work proposes to extend the simulations to heterogeneous materials. As a first step, heterogeneous materials can be simulated with a simple model of ductile atoms where a user-defined fraction of the ductile atoms are replaced at random by brittle atoms. From this model, a mixture law for shear strength can be established. Length scale effects on shear strength appear and impact the debris formation. This model could then be used as a baseline for more structured and realistic heterogeneous materials.